1. Field of the Invention
The present invention relates to a variable delivery compressor with reciprocatory pistons, adapted mainly for use in an air conditioning system of a vehicle.
2. Description of the Related Art
Many types of variable delivery compressors are known, such as a typical variable compressor with reciprocatory double-acting pistons disclosed in U.S. Pat. No. 4,403,921 to Kato et al. This variable delivery compressor is provided with a delivery valve capable of moving between a first full delivery position and a second reduced delivery position in response to a change in a cooling load requirement, and a valve is arranged adjacent to a delivery flange to prevent the compressed refrigerant from being circulated within the compressor per se when the compressor is operated at a reduced delivery state. The delivery valve comprises a valve member and a spool member having a front end face to which the valve member is fixed, and a rear end face formed as a pressure receiving surface. The spool member is slidable so that the valve member can move from the first full delivery position to the second reduced delivery position, and vice versa. The above-mentioned valve member is formed as a check valve.
In the above-mentioned variable delivery compressor, because the check valve is employed, a problem arises in that the refrigerant delivery mechanism of the compressor becomes complicated. Further, since the delivery flange of the compressor must receive the check valve, the size of the delivery flange must be such that it is difficult to find a space for mounting a compressor having such a delivery flange in a small engine compartment of a vehicle.
Also, when the operation of the compressor is switched from full delivery to reduced delivery, a part of the compressed refrigerant under a high temperature and high pressure is temporarily returned directly from the delivery side of the compressor to the suction side thereof, and as a result, the compression efficiency is reduced. In addition, during the reduced delivery operation of the compressor, while some compression chambers, i.e., the compression chambers on the axially rear side of the compressor, are supplied with the refrigerant gas to be conpressed through both suction and discharge ports of the valve plate of the compressor, the delivery of the refrigerant due to compressive action of the pistons is permitted to pass through only the discharge port. As a result, it is impossible to evacuate all of the refrigerant gas from the compression chambers on the rear side. Therefore, an excessive load is applied to the vehicle engine when driving the compressor, and consequently, a loss of power of the vehicle engine cannot be avoided at a high speed driving condition of the vehicle.